/**
 * @file
 * Dynamic Host Configuration Protocol client
 *
 * @defgroup dhcp4 DHCPv4
 * @ingroup ip4
 * DHCP (IPv4) related functions
 * This is a DHCP client for the lwIP TCP/IP stack. It aims to conform
 * with RFC 2131 and RFC 2132.
 *
 * @todo:
 * - Support for interfaces other than Ethernet (SLIP, PPP, ...)
 *
 * Options:
 * @ref DHCP_COARSE_TIMER_SECS (recommended 60 which is a minute)
 * @ref DHCP_FINE_TIMER_MSECS (recommended 500 which equals TCP coarse timer)
 *
 * dhcp_start() starts a DHCP client instance which
 * configures the interface by obtaining an IP address lease and maintaining it.
 *
 * Use dhcp_release() to end the lease and use dhcp_stop()
 * to remove the DHCP client.
 *
 * @see LWIP_HOOK_DHCP_APPEND_OPTIONS
 * @see LWIP_HOOK_DHCP_PARSE_OPTION
 *
 * @see netifapi_dhcp4
 */

/*
 * Copyright (c) 2001-2004 Leon Woestenberg <leon.woestenberg@gmx.net>
 * Copyright (c) 2001-2004 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 * The Swedish Institute of Computer Science and Adam Dunkels
 * are specifically granted permission to redistribute this
 * source code.
 *
 * Author: Leon Woestenberg <leon.woestenberg@gmx.net>
 *
 */

#include "lwip/opt.h"

#if LWIP_IPV4 && LWIP_DHCP /* don't build if not configured for use in lwipopts.h */

#include "lwip/stats.h"
#include "lwip/mem.h"
#include "lwip/udp.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/def.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "lwip/dns.h"
#include "lwip/etharp.h"
#include "lwip/prot/dhcp.h"
#include "lwip/prot/iana.h"

#include <string.h>

#ifdef LWIP_HOOK_FILENAME
#include LWIP_HOOK_FILENAME
#endif
#ifndef LWIP_HOOK_DHCP_APPEND_OPTIONS
#define LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, state, msg, msg_type, options_len_ptr)
#endif
#ifndef LWIP_HOOK_DHCP_PARSE_OPTION
#define LWIP_HOOK_DHCP_PARSE_OPTION(netif, dhcp, state, msg, msg_type, option, len, pbuf, offset) \
    do                                                                                            \
    {                                                                                             \
        LWIP_UNUSED_ARG(msg);                                                                     \
    } while (0)
#endif

/** DHCP_CREATE_RAND_XID: if this is set to 1, the xid is created using
 * LWIP_RAND() (this overrides DHCP_GLOBAL_XID)
 */
#ifndef DHCP_CREATE_RAND_XID
#define DHCP_CREATE_RAND_XID 1
#endif

/** Default for DHCP_GLOBAL_XID is 0xABCD0000
 * This can be changed by defining DHCP_GLOBAL_XID and DHCP_GLOBAL_XID_HEADER, e.g.
 *  \#define DHCP_GLOBAL_XID_HEADER "stdlib.h"
 *  \#define DHCP_GLOBAL_XID rand()
 */
#ifdef DHCP_GLOBAL_XID_HEADER
#include DHCP_GLOBAL_XID_HEADER /* include optional starting XID generation prototypes */
#endif

/** DHCP_OPTION_MAX_MSG_SIZE is set to the MTU
 * MTU is checked to be big enough in dhcp_start */
#define DHCP_MAX_MSG_LEN(netif)       (netif->mtu)
#define DHCP_MAX_MSG_LEN_MIN_REQUIRED 576
/** Minimum length for reply before packet is parsed */
#define DHCP_MIN_REPLY_LEN 44

#define REBOOT_TRIES       2

#if LWIP_DNS && LWIP_DHCP_MAX_DNS_SERVERS
#if DNS_MAX_SERVERS > LWIP_DHCP_MAX_DNS_SERVERS
#define LWIP_DHCP_PROVIDE_DNS_SERVERS LWIP_DHCP_MAX_DNS_SERVERS
#else
#define LWIP_DHCP_PROVIDE_DNS_SERVERS DNS_MAX_SERVERS
#endif
#else
#define LWIP_DHCP_PROVIDE_DNS_SERVERS 0
#endif

/** Option handling: options are parsed in dhcp_parse_reply
 * and saved in an array where other functions can load them from.
 * This might be moved into the struct dhcp (not necessarily since
 * lwIP is single-threaded and the array is only used while in recv
 * callback). */
enum dhcp_option_idx
{
    DHCP_OPTION_IDX_OVERLOAD = 0,
    DHCP_OPTION_IDX_MSG_TYPE,
    DHCP_OPTION_IDX_SERVER_ID,
    DHCP_OPTION_IDX_LEASE_TIME,
    DHCP_OPTION_IDX_T1,
    DHCP_OPTION_IDX_T2,
    DHCP_OPTION_IDX_SUBNET_MASK,
    DHCP_OPTION_IDX_ROUTER,
#if LWIP_DHCP_PROVIDE_DNS_SERVERS
    DHCP_OPTION_IDX_DNS_SERVER,
    DHCP_OPTION_IDX_DNS_SERVER_LAST = DHCP_OPTION_IDX_DNS_SERVER + LWIP_DHCP_PROVIDE_DNS_SERVERS - 1,
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
#if LWIP_DHCP_GET_NTP_SRV
    DHCP_OPTION_IDX_NTP_SERVER,
    DHCP_OPTION_IDX_NTP_SERVER_LAST = DHCP_OPTION_IDX_NTP_SERVER + LWIP_DHCP_MAX_NTP_SERVERS - 1,
#endif /* LWIP_DHCP_GET_NTP_SRV */
    DHCP_OPTION_IDX_MAX
};

/** Holds the decoded option values, only valid while in dhcp_recv.
    @todo: move this into struct dhcp? */
u32_t dhcp_rx_options_val[DHCP_OPTION_IDX_MAX];
/** Holds a flag which option was received and is contained in dhcp_rx_options_val,
    only valid while in dhcp_recv.
    @todo: move this into struct dhcp? */
u8_t dhcp_rx_options_given[DHCP_OPTION_IDX_MAX];

static u8_t dhcp_discover_request_options[] = {
    DHCP_OPTION_SUBNET_MASK,
    DHCP_OPTION_ROUTER,
    DHCP_OPTION_BROADCAST
#if LWIP_DHCP_PROVIDE_DNS_SERVERS
    ,
    DHCP_OPTION_DNS_SERVER
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
#if LWIP_DHCP_GET_NTP_SRV
    ,
    DHCP_OPTION_NTP
#endif /* LWIP_DHCP_GET_NTP_SRV */
};

#ifdef DHCP_GLOBAL_XID
static u32_t xid;
static u8_t xid_initialised;
#endif /* DHCP_GLOBAL_XID */

#define dhcp_option_given(dhcp, idx)          (dhcp_rx_options_given[idx] != 0)
#define dhcp_got_option(dhcp, idx)            (dhcp_rx_options_given[idx] = 1)
#define dhcp_clear_option(dhcp, idx)          (dhcp_rx_options_given[idx] = 0)
#define dhcp_clear_all_options(dhcp)          (memset(dhcp_rx_options_given, 0, sizeof(dhcp_rx_options_given)))
#define dhcp_get_option_value(dhcp, idx)      (dhcp_rx_options_val[idx])
#define dhcp_set_option_value(dhcp, idx, val) (dhcp_rx_options_val[idx] = (val))

static struct udp_pcb* dhcp_pcb;
static u8_t dhcp_pcb_refcount;

/* DHCP client state machine functions */
static err_t dhcp_discover(struct netif* netif);
static err_t dhcp_select(struct netif* netif);
static void dhcp_bind(struct netif* netif);
#if DHCP_DOES_ARP_CHECK
static err_t dhcp_decline(struct netif* netif);
#endif /* DHCP_DOES_ARP_CHECK */
static err_t dhcp_rebind(struct netif* netif);
static err_t dhcp_reboot(struct netif* netif);
static void dhcp_set_state(struct dhcp* dhcp, u8_t new_state);

/* receive, unfold, parse and free incoming messages */
static void dhcp_recv(void* arg, struct udp_pcb* pcb, struct pbuf* p, const ip_addr_t* addr, u16_t port);

/* set the DHCP timers */
static void dhcp_timeout(struct netif* netif);
static void dhcp_t1_timeout(struct netif* netif);
static void dhcp_t2_timeout(struct netif* netif);

/* build outgoing messages */
/* create a DHCP message, fill in common headers */
static struct pbuf* dhcp_create_msg(struct netif* netif, struct dhcp* dhcp, u8_t message_type, u16_t* options_out_len);
/* add a DHCP option (type, then length in bytes) */
static u16_t dhcp_option(u16_t options_out_len, u8_t* options, u8_t option_type, u8_t option_len);
/* add option values */
static u16_t dhcp_option_byte(u16_t options_out_len, u8_t* options, u8_t value);
static u16_t dhcp_option_short(u16_t options_out_len, u8_t* options, u16_t value);
static u16_t dhcp_option_long(u16_t options_out_len, u8_t* options, u32_t value);
#if LWIP_NETIF_HOSTNAME
static u16_t dhcp_option_hostname(u16_t options_out_len, u8_t* options, struct netif* netif);
#endif /* LWIP_NETIF_HOSTNAME */
/* always add the DHCP options trailer to end and pad */
static void dhcp_option_trailer(u16_t options_out_len, u8_t* options, struct pbuf* p_out);

/** Ensure DHCP PCB is allocated and bound */
static err_t dhcp_inc_pcb_refcount(void)
{
    if (dhcp_pcb_refcount == 0)
    {
        LWIP_ASSERT("dhcp_inc_pcb_refcount(): memory leak", dhcp_pcb == NULL);

        /* allocate UDP PCB */
        dhcp_pcb = udp_new();

        if (dhcp_pcb == NULL)
        {
            return ERR_MEM;
        }

        ip_set_option(dhcp_pcb, SOF_BROADCAST);

        /* set up local and remote port for the pcb -> listen on all interfaces on all src/dest IPs */
        udp_bind(dhcp_pcb, IP4_ADDR_ANY, LWIP_IANA_PORT_DHCP_CLIENT);
        udp_connect(dhcp_pcb, IP4_ADDR_ANY, LWIP_IANA_PORT_DHCP_SERVER);
        udp_recv(dhcp_pcb, dhcp_recv, NULL);
    }

    dhcp_pcb_refcount++;

    return ERR_OK;
}

/** Free DHCP PCB if the last netif stops using it */
static void dhcp_dec_pcb_refcount(void)
{
    LWIP_ASSERT("dhcp_pcb_refcount(): refcount error", (dhcp_pcb_refcount > 0));
    dhcp_pcb_refcount--;

    if (dhcp_pcb_refcount == 0)
    {
        udp_remove(dhcp_pcb);
        dhcp_pcb = NULL;
    }
}

/**
 * Back-off the DHCP client (because of a received NAK response).
 *
 * Back-off the DHCP client because of a received NAK. Receiving a
 * NAK means the client asked for something non-sensible, for
 * example when it tries to renew a lease obtained on another network.
 *
 * We clear any existing set IP address and restart DHCP negotiation
 * afresh (as per RFC2131 3.2.3).
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_handle_nak(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE,
        ("dhcp_handle_nak(netif=%p) %c%c%" U16_F "\n",
         (void*)netif,
         netif->name[0],
         netif->name[1],
         (u16_t)netif->num));
    /* Change to a defined state - set this before assigning the address
       to ensure the callback can use dhcp_supplied_address() */
    dhcp_set_state(dhcp, DHCP_STATE_BACKING_OFF);
    /* remove IP address from interface (must no longer be used, as per RFC2131) */
    netif_set_addr(netif, IP4_ADDR_ANY4, IP4_ADDR_ANY4, IP4_ADDR_ANY4);
    /* We can immediately restart discovery */
    dhcp_discover(netif);
}

#if DHCP_DOES_ARP_CHECK
/**
 * Checks if the offered IP address is already in use.
 *
 * It does so by sending an ARP request for the offered address and
 * entering CHECKING state. If no ARP reply is received within a small
 * interval, the address is assumed to be free for use by us.
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_check(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    err_t result;
    u16_t msecs;
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE,
        ("dhcp_check(netif=%p) %c%c\n", (void*)netif, (s16_t)netif->name[0], (s16_t)netif->name[1]));
    dhcp_set_state(dhcp, DHCP_STATE_CHECKING);
    /* create an ARP query for the offered IP address, expecting that no host
       responds, as the IP address should not be in use. */
    result = etharp_query(netif, &dhcp->offered_ip_addr, NULL);
    if (result != ERR_OK)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
            ("dhcp_check: could not perform ARP query\n"));
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
    msecs = 500;
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
        ("dhcp_check(): set request timeout %" U16_F " msecs\n", msecs));
}
#endif /* DHCP_DOES_ARP_CHECK */

/**
 * Remember the configuration offered by a DHCP server.
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_handle_offer(struct netif* netif, struct dhcp_msg* msg_in)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE,
        ("dhcp_handle_offer(netif=%p) %c%c%" U16_F "\n",
         (void*)netif,
         netif->name[0],
         netif->name[1],
         (u16_t)netif->num));
    /* obtain the server address */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_SERVER_ID))
    {
        dhcp->request_timeout = 0; /* stop timer */

        ip_addr_set_ip4_u32(&dhcp->server_ip_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_SERVER_ID)));
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_STATE,
            ("dhcp_handle_offer(): server 0x%08" X32_F "\n", ip4_addr_get_u32(ip_2_ip4(&dhcp->server_ip_addr))));
        /* remember offered address */
        ip4_addr_copy(dhcp->offered_ip_addr, msg_in->yiaddr);
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_STATE,
            ("dhcp_handle_offer(): offer for 0x%08" X32_F "\n", ip4_addr_get_u32(&dhcp->offered_ip_addr)));

        dhcp_select(netif);
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_handle_offer(netif=%p) did not get server ID!\n", (void*)netif));
    }
}

/**
 * Select a DHCP server offer out of all offers.
 *
 * Simply select the first offer received.
 *
 * @param netif the netif under DHCP control
 * @return lwIP specific error (see error.h)
 */
static err_t dhcp_select(struct netif* netif)
{
    struct dhcp* dhcp;
    err_t result;
    u16_t msecs;
    u8_t i;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_ERROR("dhcp_select: netif != NULL", (netif != NULL), return ERR_ARG;);
    dhcp = netif_dhcp_data(netif);
    LWIP_ERROR("dhcp_select: dhcp != NULL", (dhcp != NULL), return ERR_VAL;);

    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE,
        ("dhcp_select(netif=%p) %c%c%" U16_F "\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
    dhcp_set_state(dhcp, DHCP_STATE_REQUESTING);

    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, dhcp, DHCP_REQUEST, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        options_out_len =
            dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
        options_out_len = dhcp_option_short(options_out_len, msg_out->options, DHCP_MAX_MSG_LEN(netif));

        /* MUST request the offered IP address */
        options_out_len = dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_REQUESTED_IP, 4);
        options_out_len =
            dhcp_option_long(options_out_len, msg_out->options, lwip_ntohl(ip4_addr_get_u32(&dhcp->offered_ip_addr)));

        options_out_len = dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_SERVER_ID, 4);
        options_out_len = dhcp_option_long(
            options_out_len,
            msg_out->options,
            lwip_ntohl(ip4_addr_get_u32(ip_2_ip4(&dhcp->server_ip_addr))));

        options_out_len = dhcp_option(
            options_out_len,
            msg_out->options,
            DHCP_OPTION_PARAMETER_REQUEST_LIST,
            LWIP_ARRAYSIZE(dhcp_discover_request_options));
        for (i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++)
        {
            options_out_len = dhcp_option_byte(options_out_len, msg_out->options, dhcp_discover_request_options[i]);
        }

#if LWIP_NETIF_HOSTNAME
        options_out_len = dhcp_option_hostname(options_out_len, msg_out->options, netif);
#endif /* LWIP_NETIF_HOSTNAME */

        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_REQUESTING, msg_out, DHCP_REQUEST, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        /* send broadcast to any DHCP server */
        result = udp_sendto_if_src(dhcp_pcb, p_out, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER, netif, IP4_ADDR_ANY);
        pbuf_free(p_out);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_select: REQUESTING\n"));
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
            ("dhcp_select: could not allocate DHCP request\n"));
        result = ERR_MEM;
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
    msecs = (u16_t)((dhcp->tries < 6 ? 1 << dhcp->tries : 60) * 1000);
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_select(): set request timeout %" U16_F " msecs\n", msecs));
    return result;
}

/**
 * The DHCP timer that checks for lease renewal/rebind timeouts.
 * Must be called once a minute (see @ref DHCP_COARSE_TIMER_SECS).
 */
void dhcp_coarse_tmr(void)
{
    struct netif* netif;
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_coarse_tmr()\n"));
    /* iterate through all network interfaces */
    NETIF_FOREACH(netif)
    {
        /* only act on DHCP configured interfaces */
        struct dhcp* dhcp = netif_dhcp_data(netif);
        if ((dhcp != NULL) && (dhcp->state != DHCP_STATE_OFF))
        {
            /* compare lease time to expire timeout */
            if (dhcp->t0_timeout && (++dhcp->lease_used == dhcp->t0_timeout))
            {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t0 timeout\n"));
                /* this clients' lease time has expired */
                dhcp_release_and_stop(netif);
                dhcp_start(netif);
                /* timer is active (non zero), and triggers (zeroes) now? */
            }
            else if (dhcp->t2_rebind_time && (dhcp->t2_rebind_time-- == 1))
            {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t2 timeout\n"));
                /* this clients' rebind timeout triggered */
                dhcp_t2_timeout(netif);
                /* timer is active (non zero), and triggers (zeroes) now */
            }
            else if (dhcp->t1_renew_time && (dhcp->t1_renew_time-- == 1))
            {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t1 timeout\n"));
                /* this clients' renewal timeout triggered */
                dhcp_t1_timeout(netif);
            }
        }
    }
}

/**
 * DHCP transaction timeout handling (this function must be called every 500ms,
 * see @ref DHCP_FINE_TIMER_MSECS).
 *
 * A DHCP server is expected to respond within a short period of time.
 * This timer checks whether an outstanding DHCP request is timed out.
 */
void dhcp_fine_tmr(void)
{
    struct netif* netif;
    /* loop through netif's */
    NETIF_FOREACH(netif)
    {
        struct dhcp* dhcp = netif_dhcp_data(netif);
        /* only act on DHCP configured interfaces */
        if (dhcp != NULL)
        {
            /* timer is active (non zero), and is about to trigger now */
            if (dhcp->request_timeout > 1)
            {
                dhcp->request_timeout--;
            }
            else if (dhcp->request_timeout == 1)
            {
                dhcp->request_timeout--;
                /* { dhcp->request_timeout == 0 } */
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_fine_tmr(): request timeout\n"));
                /* this client's request timeout triggered */
                dhcp_timeout(netif);
            }
        }
    }
}

/**
 * A DHCP negotiation transaction, or ARP request, has timed out.
 *
 * The timer that was started with the DHCP or ARP request has
 * timed out, indicating no response was received in time.
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_timeout(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_timeout()\n"));
    /* back-off period has passed, or server selection timed out */
    if ((dhcp->state == DHCP_STATE_BACKING_OFF) || (dhcp->state == DHCP_STATE_SELECTING))
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_timeout(): restarting discovery\n"));
        dhcp_discover(netif);
        /* receiving the requested lease timed out */
    }
    else if (dhcp->state == DHCP_STATE_REQUESTING)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
            ("dhcp_timeout(): REQUESTING, DHCP request timed out\n"));
        if (dhcp->tries <= 5)
        {
            dhcp_select(netif);
        }
        else
        {
            LWIP_DEBUGF(
                DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
                ("dhcp_timeout(): REQUESTING, releasing, restarting\n"));
            dhcp_release_and_stop(netif);
            dhcp_start(netif);
        }
#if DHCP_DOES_ARP_CHECK
        /* received no ARP reply for the offered address (which is good) */
    }
    else if (dhcp->state == DHCP_STATE_CHECKING)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
            ("dhcp_timeout(): CHECKING, ARP request timed out\n"));
        if (dhcp->tries <= 1)
        {
            dhcp_check(netif);
            /* no ARP replies on the offered address,
               looks like the IP address is indeed free */
        }
        else
        {
            /* bind the interface to the offered address */
            dhcp_bind(netif);
        }
#endif /* DHCP_DOES_ARP_CHECK */
    }
    else if (dhcp->state == DHCP_STATE_REBOOTING)
    {
        if (dhcp->tries < REBOOT_TRIES)
        {
            dhcp_reboot(netif);
        }
        else
        {
            dhcp_discover(netif);
        }
    }
}

/**
 * The renewal period has timed out.
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_t1_timeout(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_t1_timeout()\n"));
    if ((dhcp->state == DHCP_STATE_REQUESTING) || (dhcp->state == DHCP_STATE_BOUND)
        || (dhcp->state == DHCP_STATE_RENEWING))
    {
        /* just retry to renew - note that the rebind timer (t2) will
         * eventually time-out if renew tries fail. */
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t1_timeout(): must renew\n"));
        /* This slightly different to RFC2131: DHCPREQUEST will be sent from state
           DHCP_STATE_RENEWING, not DHCP_STATE_BOUND */
        dhcp_renew(netif);
        /* Calculate next timeout */
        if (((dhcp->t2_timeout - dhcp->lease_used) / 2) >= ((60 + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS))
        {
            dhcp->t1_renew_time = (u16_t)((dhcp->t2_timeout - dhcp->lease_used) / 2);
        }
    }
}

/**
 * The rebind period has timed out.
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_t2_timeout(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t2_timeout()\n"));
    if ((dhcp->state == DHCP_STATE_REQUESTING) || (dhcp->state == DHCP_STATE_BOUND)
        || (dhcp->state == DHCP_STATE_RENEWING) || (dhcp->state == DHCP_STATE_REBINDING))
    {
        /* just retry to rebind */
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t2_timeout(): must rebind\n"));
        /* This slightly different to RFC2131: DHCPREQUEST will be sent from state
           DHCP_STATE_REBINDING, not DHCP_STATE_BOUND */
        dhcp_rebind(netif);
        /* Calculate next timeout */
        if (((dhcp->t0_timeout - dhcp->lease_used) / 2) >= ((60 + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS))
        {
            dhcp->t2_rebind_time = (u16_t)((dhcp->t0_timeout - dhcp->lease_used) / 2);
        }
    }
}

/**
 * Handle a DHCP ACK packet
 *
 * @param netif the netif under DHCP control
 */
static void dhcp_handle_ack(struct netif* netif, struct dhcp_msg* msg_in)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

#if LWIP_DHCP_PROVIDE_DNS_SERVERS || LWIP_DHCP_GET_NTP_SRV
    u8_t n;
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS || LWIP_DHCP_GET_NTP_SRV */
#if LWIP_DHCP_GET_NTP_SRV
    ip4_addr_t ntp_server_addrs[LWIP_DHCP_MAX_NTP_SERVERS];
#endif

    /* clear options we might not get from the ACK */
    ip4_addr_set_zero(&dhcp->offered_sn_mask);
    ip4_addr_set_zero(&dhcp->offered_gw_addr);
#if LWIP_DHCP_BOOTP_FILE
    ip4_addr_set_zero(&dhcp->offered_si_addr);
#endif /* LWIP_DHCP_BOOTP_FILE */

    /* lease time given? */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_LEASE_TIME))
    {
        /* remember offered lease time */
        dhcp->offered_t0_lease = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_LEASE_TIME);
    }
    /* renewal period given? */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_T1))
    {
        /* remember given renewal period */
        dhcp->offered_t1_renew = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_T1);
    }
    else
    {
        /* calculate safe periods for renewal */
        dhcp->offered_t1_renew = dhcp->offered_t0_lease / 2;
    }

    /* renewal period given? */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_T2))
    {
        /* remember given rebind period */
        dhcp->offered_t2_rebind = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_T2);
    }
    else
    {
        /* calculate safe periods for rebinding (offered_t0_lease * 0.875 -> 87.5%)*/
        dhcp->offered_t2_rebind = (dhcp->offered_t0_lease * 7U) / 8U;
    }

    /* (y)our internet address */
    ip4_addr_copy(dhcp->offered_ip_addr, msg_in->yiaddr);

#if LWIP_DHCP_BOOTP_FILE
    /* copy boot server address,
       boot file name copied in dhcp_parse_reply if not overloaded */
    ip4_addr_copy(dhcp->offered_si_addr, msg_in->siaddr);
#endif /* LWIP_DHCP_BOOTP_FILE */

    /* subnet mask given? */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_SUBNET_MASK))
    {
        /* remember given subnet mask */
        ip4_addr_set_u32(&dhcp->offered_sn_mask, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_SUBNET_MASK)));
        dhcp->subnet_mask_given = 1;
    }
    else
    {
        dhcp->subnet_mask_given = 0;
    }

    /* gateway router */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_ROUTER))
    {
        ip4_addr_set_u32(&dhcp->offered_gw_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_ROUTER)));
    }

#if LWIP_DHCP_GET_NTP_SRV
    /* NTP servers */
    for (n = 0; (n < LWIP_DHCP_MAX_NTP_SERVERS) && dhcp_option_given(dhcp, DHCP_OPTION_IDX_NTP_SERVER + n); n++)
    {
        ip4_addr_set_u32(&ntp_server_addrs[n], lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_NTP_SERVER + n)));
    }
    dhcp_set_ntp_servers(n, ntp_server_addrs);
#endif /* LWIP_DHCP_GET_NTP_SRV */

#if LWIP_DHCP_PROVIDE_DNS_SERVERS
    /* DNS servers */
    for (n = 0; (n < LWIP_DHCP_PROVIDE_DNS_SERVERS) && dhcp_option_given(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n); n++)
    {
        ip_addr_t dns_addr;
        ip_addr_set_ip4_u32_val(dns_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n)));
        dns_setserver(n, &dns_addr);
    }
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
}

/**
 * @ingroup dhcp4
 * Set a statically allocated struct dhcp to work with.
 * Using this prevents dhcp_start to allocate it using mem_malloc.
 *
 * @param netif the netif for which to set the struct dhcp
 * @param dhcp (uninitialised) dhcp struct allocated by the application
 */
void dhcp_set_struct(struct netif* netif, struct dhcp* dhcp)
{
    LWIP_ASSERT_CORE_LOCKED();
    LWIP_ASSERT("netif != NULL", netif != NULL);
    LWIP_ASSERT("dhcp != NULL", dhcp != NULL);
    LWIP_ASSERT("netif already has a struct dhcp set", netif_dhcp_data(netif) == NULL);

    /* clear data structure */
    memset(dhcp, 0, sizeof(struct dhcp));
    /* dhcp_set_state(&dhcp, DHCP_STATE_OFF); */
    netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCP, dhcp);
}

/**
 * @ingroup dhcp4
 * Removes a struct dhcp from a netif.
 *
 * ATTENTION: Only use this when not using dhcp_set_struct() to allocate the
 *            struct dhcp since the memory is passed back to the heap.
 *
 * @param netif the netif from which to remove the struct dhcp
 */
void dhcp_cleanup(struct netif* netif)
{
    LWIP_ASSERT_CORE_LOCKED();
    LWIP_ASSERT("netif != NULL", netif != NULL);

    if (netif_dhcp_data(netif) != NULL)
    {
        mem_free(netif_dhcp_data(netif));
        netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCP, NULL);
    }
}

/**
 * @ingroup dhcp4
 * Start DHCP negotiation for a network interface.
 *
 * If no DHCP client instance was attached to this interface,
 * a new client is created first. If a DHCP client instance
 * was already present, it restarts negotiation.
 *
 * @param netif The lwIP network interface
 * @return lwIP error code
 * - ERR_OK - No error
 * - ERR_MEM - Out of memory
 */
err_t dhcp_start(struct netif* netif)
{
    struct dhcp* dhcp;
    err_t result;

    LWIP_ASSERT_CORE_LOCKED();
    LWIP_ERROR("netif != NULL", (netif != NULL), return ERR_ARG;);
    LWIP_ERROR("netif is not up, old style port?", netif_is_up(netif), return ERR_ARG;);
    dhcp = netif_dhcp_data(netif);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
        ("dhcp_start(netif=%p) %c%c%" U16_F "\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));

    /* check MTU of the netif */
    if (netif->mtu < DHCP_MAX_MSG_LEN_MIN_REQUIRED)
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): Cannot use this netif with DHCP: MTU is too small\n"));
        return ERR_MEM;
    }

    /* no DHCP client attached yet? */
    if (dhcp == NULL)
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): mallocing new DHCP client\n"));
        dhcp = (struct dhcp*)mem_malloc(sizeof(struct dhcp));
        if (dhcp == NULL)
        {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): could not allocate dhcp\n"));
            return ERR_MEM;
        }

        /* store this dhcp client in the netif */
        netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCP, dhcp);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): allocated dhcp"));
        /* already has DHCP client attached */
    }
    else
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_start(): restarting DHCP configuration\n"));

        if (dhcp->pcb_allocated != 0)
        {
            dhcp_dec_pcb_refcount(); /* free DHCP PCB if not needed any more */
        }
        /* dhcp is cleared below, no need to reset flag*/
    }

    /* clear data structure */
    memset(dhcp, 0, sizeof(struct dhcp));
    /* dhcp_set_state(&dhcp, DHCP_STATE_OFF); */

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting DHCP configuration\n"));

    if (dhcp_inc_pcb_refcount() != ERR_OK)
    { /* ensure DHCP PCB is allocated */
        return ERR_MEM;
    }
    dhcp->pcb_allocated = 1;

    if (!netif_is_link_up(netif))
    {
        /* set state INIT and wait for dhcp_network_changed() to call dhcp_discover() */
        dhcp_set_state(dhcp, DHCP_STATE_INIT);
        return ERR_OK;
    }

    /* (re)start the DHCP negotiation */
    result = dhcp_discover(netif);
    if (result != ERR_OK)
    {
        /* free resources allocated above */
        dhcp_release_and_stop(netif);
        return ERR_MEM;
    }
    return result;
}

/**
 * @ingroup dhcp4
 * Inform a DHCP server of our manual configuration.
 *
 * This informs DHCP servers of our fixed IP address configuration
 * by sending an INFORM message. It does not involve DHCP address
 * configuration, it is just here to be nice to the network.
 *
 * @param netif The lwIP network interface
 */
void dhcp_inform(struct netif* netif)
{
    struct dhcp dhcp;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_ASSERT_CORE_LOCKED();
    LWIP_ERROR("netif != NULL", (netif != NULL), return;);

    if (dhcp_inc_pcb_refcount() != ERR_OK)
    { /* ensure DHCP PCB is allocated */
        return;
    }

    memset(&dhcp, 0, sizeof(struct dhcp));
    dhcp_set_state(&dhcp, DHCP_STATE_INFORMING);

    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, &dhcp, DHCP_INFORM, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        options_out_len =
            dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
        options_out_len = dhcp_option_short(options_out_len, msg_out->options, DHCP_MAX_MSG_LEN(netif));

        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, &dhcp, DHCP_STATE_INFORMING, msg_out, DHCP_INFORM, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_inform: INFORMING\n"));

        udp_sendto_if(dhcp_pcb, p_out, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER, netif);

        pbuf_free(p_out);
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_inform: could not allocate DHCP request\n"));
    }

    dhcp_dec_pcb_refcount(); /* delete DHCP PCB if not needed any more */
}

/** Handle a possible change in the network configuration.
 *
 * This enters the REBOOTING state to verify that the currently bound
 * address is still valid.
 */
void dhcp_network_changed(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);

    if (!dhcp)
    {
        return;
    }
    switch (dhcp->state)
    {
    case DHCP_STATE_REBINDING:
    case DHCP_STATE_RENEWING:
    case DHCP_STATE_BOUND:
    case DHCP_STATE_REBOOTING:
        dhcp->tries = 0;
        dhcp_reboot(netif);
        break;
    case DHCP_STATE_OFF:
        /* stay off */
        break;
    default:
        LWIP_ASSERT("invalid dhcp->state", dhcp->state <= DHCP_STATE_BACKING_OFF);
        /* INIT/REQUESTING/CHECKING/BACKING_OFF restart with new 'rid' because the
           state changes, SELECTING: continue with current 'rid' as we stay in the
           same state */
#if LWIP_DHCP_AUTOIP_COOP
        if (dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON)
        {
            autoip_stop(netif);
            dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
        }
#endif /* LWIP_DHCP_AUTOIP_COOP */
        /* ensure we start with short timeouts, even if already discovering */
        dhcp->tries = 0;
        dhcp_discover(netif);
        break;
    }
}

#if DHCP_DOES_ARP_CHECK
/**
 * Match an ARP reply with the offered IP address:
 * check whether the offered IP address is not in use using ARP
 *
 * @param netif the network interface on which the reply was received
 * @param addr The IP address we received a reply from
 */
void dhcp_arp_reply(struct netif* netif, const ip4_addr_t* addr)
{
    struct dhcp* dhcp;

    LWIP_ERROR("netif != NULL", (netif != NULL), return;);
    dhcp = netif_dhcp_data(netif);
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_arp_reply()\n"));
    /* is a DHCP client doing an ARP check? */
    if ((dhcp != NULL) && (dhcp->state == DHCP_STATE_CHECKING))
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
            ("dhcp_arp_reply(): CHECKING, arp reply for 0x%08" X32_F "\n", ip4_addr_get_u32(addr)));
        /* did a host respond with the address we
           were offered by the DHCP server? */
        if (ip4_addr_cmp(addr, &dhcp->offered_ip_addr))
        {
            /* we will not accept the offered address */
            LWIP_DEBUGF(
                DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE | LWIP_DBG_LEVEL_WARNING,
                ("dhcp_arp_reply(): arp reply matched with offered address, declining\n"));
            dhcp_decline(netif);
        }
    }
}

/**
 * Decline an offered lease.
 *
 * Tell the DHCP server we do not accept the offered address.
 * One reason to decline the lease is when we find out the address
 * is already in use by another host (through ARP).
 *
 * @param netif the netif under DHCP control
 */
static err_t dhcp_decline(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    err_t result;
    u16_t msecs;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_decline()\n"));
    dhcp_set_state(dhcp, DHCP_STATE_BACKING_OFF);
    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, dhcp, DHCP_DECLINE, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        options_out_len = dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_REQUESTED_IP, 4);
        options_out_len =
            dhcp_option_long(options_out_len, msg_out->options, lwip_ntohl(ip4_addr_get_u32(&dhcp->offered_ip_addr)));

        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_BACKING_OFF, msg_out, DHCP_DECLINE, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        /* per section 4.4.4, broadcast DECLINE messages */
        result = udp_sendto_if_src(dhcp_pcb, p_out, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER, netif, IP4_ADDR_ANY);
        pbuf_free(p_out);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_decline: BACKING OFF\n"));
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_decline: could not allocate DHCP request\n"));
        result = ERR_MEM;
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
    msecs = 10 * 1000;
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_decline(): set request timeout %" U16_F " msecs\n", msecs));
    return result;
}
#endif /* DHCP_DOES_ARP_CHECK */

/**
 * Start the DHCP process, discover a DHCP server.
 *
 * @param netif the netif under DHCP control
 */
static err_t dhcp_discover(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    err_t result = ERR_OK;
    u16_t msecs;
    u8_t i;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover()\n"));

    ip4_addr_set_any(&dhcp->offered_ip_addr);
    dhcp_set_state(dhcp, DHCP_STATE_SELECTING);
    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, dhcp, DHCP_DISCOVER, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: making request\n"));

        options_out_len =
            dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
        options_out_len = dhcp_option_short(options_out_len, msg_out->options, DHCP_MAX_MSG_LEN(netif));

        options_out_len = dhcp_option(
            options_out_len,
            msg_out->options,
            DHCP_OPTION_PARAMETER_REQUEST_LIST,
            LWIP_ARRAYSIZE(dhcp_discover_request_options));
        for (i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++)
        {
            options_out_len = dhcp_option_byte(options_out_len, msg_out->options, dhcp_discover_request_options[i]);
        }
        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_SELECTING, msg_out, DHCP_DISCOVER, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE,
            ("dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER)\n"));
        udp_sendto_if_src(dhcp_pcb, p_out, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER, netif, IP4_ADDR_ANY);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: deleting()ing\n"));
        pbuf_free(p_out);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_discover: SELECTING\n"));
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_discover: could not allocate DHCP request\n"));
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
#if LWIP_DHCP_AUTOIP_COOP
    if (dhcp->tries >= LWIP_DHCP_AUTOIP_COOP_TRIES && dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_OFF)
    {
        dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_ON;
        autoip_start(netif);
    }
#endif /* LWIP_DHCP_AUTOIP_COOP */
    msecs = (u16_t)((dhcp->tries < 6 ? 1 << dhcp->tries : 60) * 1000);
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
        ("dhcp_discover(): set request timeout %" U16_F " msecs\n", msecs));
    return result;
}

/**
 * Bind the interface to the offered IP address.
 *
 * @param netif network interface to bind to the offered address
 */
static void dhcp_bind(struct netif* netif)
{
    u32_t timeout;
    struct dhcp* dhcp;
    ip4_addr_t sn_mask, gw_addr;
    LWIP_ERROR("dhcp_bind: netif != NULL", (netif != NULL), return;);
    dhcp = netif_dhcp_data(netif);
    LWIP_ERROR("dhcp_bind: dhcp != NULL", (dhcp != NULL), return;);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE,
        ("dhcp_bind(netif=%p) %c%c%" U16_F "\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));

    /* reset time used of lease */
    dhcp->lease_used = 0;

    if (dhcp->offered_t0_lease != 0xffffffffUL)
    {
        /* set renewal period timer */
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE,
            ("dhcp_bind(): t0 renewal timer %" U32_F " secs\n", dhcp->offered_t0_lease));
        timeout = (dhcp->offered_t0_lease + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;
        if (timeout > 0xffff)
        {
            timeout = 0xffff;
        }
        dhcp->t0_timeout = (u16_t)timeout;
        if (dhcp->t0_timeout == 0)
        {
            dhcp->t0_timeout = 1;
        }
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
            ("dhcp_bind(): set request timeout %" U32_F " msecs\n", dhcp->offered_t0_lease * 1000));
    }

    /* temporary DHCP lease? */
    if (dhcp->offered_t1_renew != 0xffffffffUL)
    {
        /* set renewal period timer */
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE,
            ("dhcp_bind(): t1 renewal timer %" U32_F " secs\n", dhcp->offered_t1_renew));
        timeout = (dhcp->offered_t1_renew + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;
        if (timeout > 0xffff)
        {
            timeout = 0xffff;
        }
        dhcp->t1_timeout = (u16_t)timeout;
        if (dhcp->t1_timeout == 0)
        {
            dhcp->t1_timeout = 1;
        }
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
            ("dhcp_bind(): set request timeout %" U32_F " msecs\n", dhcp->offered_t1_renew * 1000));
        dhcp->t1_renew_time = dhcp->t1_timeout;
    }
    /* set renewal period timer */
    if (dhcp->offered_t2_rebind != 0xffffffffUL)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE,
            ("dhcp_bind(): t2 rebind timer %" U32_F " secs\n", dhcp->offered_t2_rebind));
        timeout = (dhcp->offered_t2_rebind + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;
        if (timeout > 0xffff)
        {
            timeout = 0xffff;
        }
        dhcp->t2_timeout = (u16_t)timeout;
        if (dhcp->t2_timeout == 0)
        {
            dhcp->t2_timeout = 1;
        }
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
            ("dhcp_bind(): set request timeout %" U32_F " msecs\n", dhcp->offered_t2_rebind * 1000));
        dhcp->t2_rebind_time = dhcp->t2_timeout;
    }

    /* If we have sub 1 minute lease, t2 and t1 will kick in at the same time. */
    if ((dhcp->t1_timeout >= dhcp->t2_timeout) && (dhcp->t2_timeout > 0))
    {
        dhcp->t1_timeout = 0;
    }

    if (dhcp->subnet_mask_given)
    {
        /* copy offered network mask */
        ip4_addr_copy(sn_mask, dhcp->offered_sn_mask);
    }
    else
    {
        /* subnet mask not given, choose a safe subnet mask given the network class */
        u8_t first_octet = ip4_addr1(&dhcp->offered_ip_addr);
        if (first_octet <= 127)
        {
            ip4_addr_set_u32(&sn_mask, PP_HTONL(0xff000000UL));
        }
        else if (first_octet >= 192)
        {
            ip4_addr_set_u32(&sn_mask, PP_HTONL(0xffffff00UL));
        }
        else
        {
            ip4_addr_set_u32(&sn_mask, PP_HTONL(0xffff0000UL));
        }
    }

    ip4_addr_copy(gw_addr, dhcp->offered_gw_addr);
    /* gateway address not given? */
    if (ip4_addr_isany_val(gw_addr))
    {
        /* copy network address */
        ip4_addr_get_network(&gw_addr, &dhcp->offered_ip_addr, &sn_mask);
        /* use first host address on network as gateway */
        ip4_addr_set_u32(&gw_addr, ip4_addr_get_u32(&gw_addr) | PP_HTONL(0x00000001UL));
    }

#if LWIP_DHCP_AUTOIP_COOP
    if (dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON)
    {
        autoip_stop(netif);
        dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
    }
#endif /* LWIP_DHCP_AUTOIP_COOP */

    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_STATE,
        ("dhcp_bind(): IP: 0x%08" X32_F " SN: 0x%08" X32_F " GW: 0x%08" X32_F "\n",
         ip4_addr_get_u32(&dhcp->offered_ip_addr),
         ip4_addr_get_u32(&sn_mask),
         ip4_addr_get_u32(&gw_addr)));
    /* netif is now bound to DHCP leased address - set this before assigning the address
       to ensure the callback can use dhcp_supplied_address() */
    dhcp_set_state(dhcp, DHCP_STATE_BOUND);

    netif_set_addr(netif, &dhcp->offered_ip_addr, &sn_mask, &gw_addr);
    /* interface is used by routing now that an address is set */
}

/**
 * @ingroup dhcp4
 * Renew an existing DHCP lease at the involved DHCP server.
 *
 * @param netif network interface which must renew its lease
 */
err_t dhcp_renew(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    err_t result;
    u16_t msecs;
    u8_t i;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_ASSERT_CORE_LOCKED();
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_renew()\n"));
    dhcp_set_state(dhcp, DHCP_STATE_RENEWING);

    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, dhcp, DHCP_REQUEST, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        options_out_len =
            dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
        options_out_len = dhcp_option_short(options_out_len, msg_out->options, DHCP_MAX_MSG_LEN(netif));

        options_out_len = dhcp_option(
            options_out_len,
            msg_out->options,
            DHCP_OPTION_PARAMETER_REQUEST_LIST,
            LWIP_ARRAYSIZE(dhcp_discover_request_options));
        for (i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++)
        {
            options_out_len = dhcp_option_byte(options_out_len, msg_out->options, dhcp_discover_request_options[i]);
        }

#if LWIP_NETIF_HOSTNAME
        options_out_len = dhcp_option_hostname(options_out_len, msg_out->options, netif);
#endif /* LWIP_NETIF_HOSTNAME */

        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_RENEWING, msg_out, DHCP_REQUEST, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        result = udp_sendto_if(dhcp_pcb, p_out, &dhcp->server_ip_addr, LWIP_IANA_PORT_DHCP_SERVER, netif);
        pbuf_free(p_out);

        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_renew: RENEWING\n"));
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_renew: could not allocate DHCP request\n"));
        result = ERR_MEM;
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
    /* back-off on retries, but to a maximum of 20 seconds */
    msecs = (u16_t)(dhcp->tries < 10 ? dhcp->tries * 2000 : 20 * 1000);
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
        ("dhcp_renew(): set request timeout %" U16_F " msecs\n", msecs));
    return result;
}

/**
 * Rebind with a DHCP server for an existing DHCP lease.
 *
 * @param netif network interface which must rebind with a DHCP server
 */
static err_t dhcp_rebind(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    err_t result;
    u16_t msecs;
    u8_t i;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind()\n"));
    dhcp_set_state(dhcp, DHCP_STATE_REBINDING);

    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, dhcp, DHCP_REQUEST, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        options_out_len =
            dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
        options_out_len = dhcp_option_short(options_out_len, msg_out->options, DHCP_MAX_MSG_LEN(netif));

        options_out_len = dhcp_option(
            options_out_len,
            msg_out->options,
            DHCP_OPTION_PARAMETER_REQUEST_LIST,
            LWIP_ARRAYSIZE(dhcp_discover_request_options));
        for (i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++)
        {
            options_out_len = dhcp_option_byte(options_out_len, msg_out->options, dhcp_discover_request_options[i]);
        }

#if LWIP_NETIF_HOSTNAME
        options_out_len = dhcp_option_hostname(options_out_len, msg_out->options, netif);
#endif /* LWIP_NETIF_HOSTNAME */

        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_REBINDING, msg_out, DHCP_DISCOVER, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        /* broadcast to server */
        result = udp_sendto_if(dhcp_pcb, p_out, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER, netif);
        pbuf_free(p_out);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind: REBINDING\n"));
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_rebind: could not allocate DHCP request\n"));
        result = ERR_MEM;
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
    msecs = (u16_t)(dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000);
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
        ("dhcp_rebind(): set request timeout %" U16_F " msecs\n", msecs));
    return result;
}

/**
 * Enter REBOOTING state to verify an existing lease
 *
 * @param netif network interface which must reboot
 */
static err_t dhcp_reboot(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    err_t result;
    u16_t msecs;
    u8_t i;
    struct pbuf* p_out;
    u16_t options_out_len;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot()\n"));
    dhcp_set_state(dhcp, DHCP_STATE_REBOOTING);

    /* create and initialize the DHCP message header */
    p_out = dhcp_create_msg(netif, dhcp, DHCP_REQUEST, &options_out_len);
    if (p_out != NULL)
    {
        struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
        options_out_len =
            dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
        options_out_len = dhcp_option_short(options_out_len, msg_out->options, DHCP_MAX_MSG_LEN_MIN_REQUIRED);

        options_out_len = dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_REQUESTED_IP, 4);
        options_out_len =
            dhcp_option_long(options_out_len, msg_out->options, lwip_ntohl(ip4_addr_get_u32(&dhcp->offered_ip_addr)));

        options_out_len = dhcp_option(
            options_out_len,
            msg_out->options,
            DHCP_OPTION_PARAMETER_REQUEST_LIST,
            LWIP_ARRAYSIZE(dhcp_discover_request_options));
        for (i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++)
        {
            options_out_len = dhcp_option_byte(options_out_len, msg_out->options, dhcp_discover_request_options[i]);
        }

#if LWIP_NETIF_HOSTNAME
        options_out_len = dhcp_option_hostname(options_out_len, msg_out->options, netif);
#endif /* LWIP_NETIF_HOSTNAME */

        LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, DHCP_STATE_REBOOTING, msg_out, DHCP_REQUEST, &options_out_len);
        dhcp_option_trailer(options_out_len, msg_out->options, p_out);

        /* broadcast to server */
        result = udp_sendto_if(dhcp_pcb, p_out, IP_ADDR_BROADCAST, LWIP_IANA_PORT_DHCP_SERVER, netif);
        pbuf_free(p_out);
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot: REBOOTING\n"));
    }
    else
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_reboot: could not allocate DHCP request\n"));
        result = ERR_MEM;
    }
    if (dhcp->tries < 255)
    {
        dhcp->tries++;
    }
    msecs = (u16_t)(dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000);
    dhcp->request_timeout = (u16_t)((msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS);
    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
        ("dhcp_reboot(): set request timeout %" U16_F " msecs\n", msecs));
    return result;
}

/**
 * @ingroup dhcp4
 * Release a DHCP lease and stop DHCP statemachine (and AUTOIP if LWIP_DHCP_AUTOIP_COOP).
 *
 * @param netif network interface
 */
void dhcp_release_and_stop(struct netif* netif)
{
    struct dhcp* dhcp = netif_dhcp_data(netif);
    ip_addr_t server_ip_addr;

    LWIP_ASSERT_CORE_LOCKED();
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_release_and_stop()\n"));
    if (dhcp == NULL)
    {
        return;
    }

    /* already off? -> nothing to do */
    if (dhcp->state == DHCP_STATE_OFF)
    {
        return;
    }

    ip_addr_copy(server_ip_addr, dhcp->server_ip_addr);

    /* clean old DHCP offer */
    ip_addr_set_zero_ip4(&dhcp->server_ip_addr);
    ip4_addr_set_zero(&dhcp->offered_ip_addr);
    ip4_addr_set_zero(&dhcp->offered_sn_mask);
    ip4_addr_set_zero(&dhcp->offered_gw_addr);
#if LWIP_DHCP_BOOTP_FILE
    ip4_addr_set_zero(&dhcp->offered_si_addr);
#endif /* LWIP_DHCP_BOOTP_FILE */
    dhcp->offered_t0_lease = dhcp->offered_t1_renew = dhcp->offered_t2_rebind = 0;
    dhcp->t1_renew_time = dhcp->t2_rebind_time = dhcp->lease_used = dhcp->t0_timeout = 0;

    /* send release message when current IP was assigned via DHCP */
    if (dhcp_supplied_address(netif))
    {
        /* create and initialize the DHCP message header */
        struct pbuf* p_out;
        u16_t options_out_len;
        p_out = dhcp_create_msg(netif, dhcp, DHCP_RELEASE, &options_out_len);
        if (p_out != NULL)
        {
            struct dhcp_msg* msg_out = (struct dhcp_msg*)p_out->payload;
            options_out_len = dhcp_option(options_out_len, msg_out->options, DHCP_OPTION_SERVER_ID, 4);
            options_out_len = dhcp_option_long(
                options_out_len,
                msg_out->options,
                lwip_ntohl(ip4_addr_get_u32(ip_2_ip4(&server_ip_addr))));

            LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, dhcp->state, msg_out, DHCP_RELEASE, &options_out_len);
            dhcp_option_trailer(options_out_len, msg_out->options, p_out);

            udp_sendto_if(dhcp_pcb, p_out, &server_ip_addr, LWIP_IANA_PORT_DHCP_SERVER, netif);
            pbuf_free(p_out);
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_release: RELEASED, DHCP_STATE_OFF\n"));
        }
        else
        {
            /* sending release failed, but that's not a problem since the correct behaviour of dhcp does not rely on
             * release */
            LWIP_DEBUGF(
                DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
                ("dhcp_release: could not allocate DHCP request\n"));
        }
    }

    /* remove IP address from interface (prevents routing from selecting this interface) */
    netif_set_addr(netif, IP4_ADDR_ANY4, IP4_ADDR_ANY4, IP4_ADDR_ANY4);

#if LWIP_DHCP_AUTOIP_COOP
    if (dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON)
    {
        autoip_stop(netif);
        dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
    }
#endif /* LWIP_DHCP_AUTOIP_COOP */

    dhcp_set_state(dhcp, DHCP_STATE_OFF);

    if (dhcp->pcb_allocated != 0)
    {
        dhcp_dec_pcb_refcount(); /* free DHCP PCB if not needed any more */
        dhcp->pcb_allocated = 0;
    }
}

/**
 * @ingroup dhcp4
 * This function calls dhcp_release_and_stop() internally.
 * @deprecated Use dhcp_release_and_stop() instead.
 */
err_t dhcp_release(struct netif* netif)
{
    dhcp_release_and_stop(netif);
    return ERR_OK;
}

/**
 * @ingroup dhcp4
 * This function calls dhcp_release_and_stop() internally.
 * @deprecated Use dhcp_release_and_stop() instead.
 */
void dhcp_stop(struct netif* netif)
{
    dhcp_release_and_stop(netif);
}

/*
 * Set the DHCP state of a DHCP client.
 *
 * If the state changed, reset the number of tries.
 */
static void dhcp_set_state(struct dhcp* dhcp, u8_t new_state)
{
    if (new_state != dhcp->state)
    {
        dhcp->state = new_state;
        dhcp->tries = 0;
        dhcp->request_timeout = 0;
    }
}

/*
 * Concatenate an option type and length field to the outgoing
 * DHCP message.
 *
 */
static u16_t dhcp_option(u16_t options_out_len, u8_t* options, u8_t option_type, u8_t option_len)
{
    LWIP_ASSERT(
        "dhcp_option: options_out_len + 2 + option_len <= DHCP_OPTIONS_LEN",
        options_out_len + 2U + option_len <= DHCP_OPTIONS_LEN);
    options[options_out_len++] = option_type;
    options[options_out_len++] = option_len;
    return options_out_len;
}
/*
 * Concatenate a single byte to the outgoing DHCP message.
 *
 */
static u16_t dhcp_option_byte(u16_t options_out_len, u8_t* options, u8_t value)
{
    LWIP_ASSERT("dhcp_option_byte: options_out_len < DHCP_OPTIONS_LEN", options_out_len < DHCP_OPTIONS_LEN);
    options[options_out_len++] = value;
    return options_out_len;
}

static u16_t dhcp_option_short(u16_t options_out_len, u8_t* options, u16_t value)
{
    LWIP_ASSERT("dhcp_option_short: options_out_len + 2 <= DHCP_OPTIONS_LEN", options_out_len + 2U <= DHCP_OPTIONS_LEN);
    options[options_out_len++] = (u8_t)((value & 0xff00U) >> 8);
    options[options_out_len++] = (u8_t)(value & 0x00ffU);
    return options_out_len;
}

static u16_t dhcp_option_long(u16_t options_out_len, u8_t* options, u32_t value)
{
    LWIP_ASSERT("dhcp_option_long: options_out_len + 4 <= DHCP_OPTIONS_LEN", options_out_len + 4U <= DHCP_OPTIONS_LEN);
    options[options_out_len++] = (u8_t)((value & 0xff000000UL) >> 24);
    options[options_out_len++] = (u8_t)((value & 0x00ff0000UL) >> 16);
    options[options_out_len++] = (u8_t)((value & 0x0000ff00UL) >> 8);
    options[options_out_len++] = (u8_t)((value & 0x000000ffUL));
    return options_out_len;
}

#if LWIP_NETIF_HOSTNAME
static u16_t dhcp_option_hostname(u16_t options_out_len, u8_t* options, struct netif* netif)
{
    if (netif->hostname != NULL)
    {
        size_t namelen = strlen(netif->hostname);
        if (namelen > 0)
        {
            size_t len;
            const char* p = netif->hostname;
            /* Shrink len to available bytes (need 2 bytes for OPTION_HOSTNAME
               and 1 byte for trailer) */
            size_t available = DHCP_OPTIONS_LEN - options_out_len - 3;
            LWIP_ASSERT("DHCP: hostname is too long!", namelen <= available);
            len = LWIP_MIN(namelen, available);
            LWIP_ASSERT("DHCP: hostname is too long!", len <= 0xFF);
            options_out_len = dhcp_option(options_out_len, options, DHCP_OPTION_HOSTNAME, (u8_t)len);
            while (len--)
            {
                options_out_len = dhcp_option_byte(options_out_len, options, *p++);
            }
        }
    }
    return options_out_len;
}
#endif /* LWIP_NETIF_HOSTNAME */

/**
 * Extract the DHCP message and the DHCP options.
 *
 * Extract the DHCP message and the DHCP options, each into a contiguous
 * piece of memory. As a DHCP message is variable sized by its options,
 * and also allows overriding some fields for options, the easy approach
 * is to first unfold the options into a contiguous piece of memory, and
 * use that further on.
 *
 */
static err_t dhcp_parse_reply(struct pbuf* p, struct dhcp* dhcp)
{
    u8_t* options;
    u16_t offset;
    u16_t offset_max;
    u16_t options_idx;
    u16_t options_idx_max;
    struct pbuf* q;
    int parse_file_as_options = 0;
    int parse_sname_as_options = 0;
    struct dhcp_msg* msg_in;
#if LWIP_DHCP_BOOTP_FILE
    int file_overloaded = 0;
#endif

    LWIP_UNUSED_ARG(dhcp);

    /* clear received options */
    dhcp_clear_all_options(dhcp);
    /* check that beginning of dhcp_msg (up to and including chaddr) is in first pbuf */
    if (p->len < DHCP_SNAME_OFS)
    {
        return ERR_BUF;
    }
    msg_in = (struct dhcp_msg*)p->payload;
#if LWIP_DHCP_BOOTP_FILE
    /* clear boot file name */
    dhcp->boot_file_name[0] = 0;
#endif /* LWIP_DHCP_BOOTP_FILE */

    /* parse options */

    /* start with options field */
    options_idx = DHCP_OPTIONS_OFS;
    /* parse options to the end of the received packet */
    options_idx_max = p->tot_len;
again:
    q = p;
    while ((q != NULL) && (options_idx >= q->len))
    {
        options_idx = (u16_t)(options_idx - q->len);
        options_idx_max = (u16_t)(options_idx_max - q->len);
        q = q->next;
    }
    if (q == NULL)
    {
        return ERR_BUF;
    }
    offset = options_idx;
    offset_max = options_idx_max;
    options = (u8_t*)q->payload;
    /* at least 1 byte to read and no end marker, then at least 3 bytes to read? */
    while ((q != NULL) && (offset < offset_max) && (options[offset] != DHCP_OPTION_END))
    {
        u8_t op = options[offset];
        u8_t len;
        u8_t decode_len = 0;
        int decode_idx = -1;
        u16_t val_offset = (u16_t)(offset + 2);
        if (val_offset < offset)
        {
            /* overflow */
            return ERR_BUF;
        }
        /* len byte might be in the next pbuf */
        if ((offset + 1) < q->len)
        {
            len = options[offset + 1];
        }
        else
        {
            len = (q->next != NULL ? ((u8_t*)q->next->payload)[0] : 0);
        }
        /* LWIP_DEBUGF(DHCP_DEBUG, ("msg_offset=%"U16_F", q->len=%"U16_F, msg_offset, q->len)); */
        decode_len = len;
        switch (op)
        {
        /* case(DHCP_OPTION_END): handled above */
        case (DHCP_OPTION_PAD):
            /* special option: no len encoded */
            decode_len = len = 0;
            /* will be increased below */
            break;
        case (DHCP_OPTION_SUBNET_MASK):
            LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_SUBNET_MASK;
            break;
        case (DHCP_OPTION_ROUTER):
            decode_len = 4; /* only copy the first given router */
            LWIP_ERROR("len >= decode_len", len >= decode_len, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_ROUTER;
            break;
#if LWIP_DHCP_PROVIDE_DNS_SERVERS
        case (DHCP_OPTION_DNS_SERVER):
            /* special case: there might be more than one server */
            LWIP_ERROR("len %% 4 == 0", len % 4 == 0, return ERR_VAL;);
            /* limit number of DNS servers */
            decode_len = LWIP_MIN(len, 4 * DNS_MAX_SERVERS);
            LWIP_ERROR("len >= decode_len", len >= decode_len, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_DNS_SERVER;
            break;
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
        case (DHCP_OPTION_LEASE_TIME):
            LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_LEASE_TIME;
            break;
#if LWIP_DHCP_GET_NTP_SRV
        case (DHCP_OPTION_NTP):
            /* special case: there might be more than one server */
            LWIP_ERROR("len %% 4 == 0", len % 4 == 0, return ERR_VAL;);
            /* limit number of NTP servers */
            decode_len = LWIP_MIN(len, 4 * LWIP_DHCP_MAX_NTP_SERVERS);
            LWIP_ERROR("len >= decode_len", len >= decode_len, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_NTP_SERVER;
            break;
#endif /* LWIP_DHCP_GET_NTP_SRV*/
        case (DHCP_OPTION_OVERLOAD):
            LWIP_ERROR("len == 1", len == 1, return ERR_VAL;);
            /* decode overload only in options, not in file/sname: invalid packet */
            LWIP_ERROR("overload in file/sname", options_idx == DHCP_OPTIONS_OFS, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_OVERLOAD;
            break;
        case (DHCP_OPTION_MESSAGE_TYPE):
            LWIP_ERROR("len == 1", len == 1, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_MSG_TYPE;
            break;
        case (DHCP_OPTION_SERVER_ID):
            LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_SERVER_ID;
            break;
        case (DHCP_OPTION_T1):
            LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_T1;
            break;
        case (DHCP_OPTION_T2):
            LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
            decode_idx = DHCP_OPTION_IDX_T2;
            break;
        default:
            decode_len = 0;
            LWIP_DEBUGF(DHCP_DEBUG, ("skipping option %" U16_F " in options\n", (u16_t)op));
            LWIP_HOOK_DHCP_PARSE_OPTION(
                ip_current_netif(),
                dhcp,
                dhcp->state,
                msg_in,
                dhcp_option_given(dhcp, DHCP_OPTION_IDX_MSG_TYPE)
                    ? (u8_t)dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_MSG_TYPE)
                    : 0,
                op,
                len,
                q,
                val_offset);
            break;
        }
        if (op == DHCP_OPTION_PAD)
        {
            offset++;
        }
        else
        {
            if (offset + len + 2 > 0xFFFF)
            {
                /* overflow */
                return ERR_BUF;
            }
            offset = (u16_t)(offset + len + 2);
            if (decode_len > 0)
            {
                u32_t value = 0;
                u16_t copy_len;
            decode_next:
                LWIP_ASSERT("check decode_idx", decode_idx >= 0 && decode_idx < DHCP_OPTION_IDX_MAX);
                if (!dhcp_option_given(dhcp, decode_idx))
                {
                    copy_len = LWIP_MIN(decode_len, 4);
                    if (pbuf_copy_partial(q, &value, copy_len, val_offset) != copy_len)
                    {
                        return ERR_BUF;
                    }
                    if (decode_len > 4)
                    {
                        /* decode more than one u32_t */
                        u16_t next_val_offset;
                        LWIP_ERROR("decode_len %% 4 == 0", decode_len % 4 == 0, return ERR_VAL;);
                        dhcp_got_option(dhcp, decode_idx);
                        dhcp_set_option_value(dhcp, decode_idx, lwip_htonl(value));
                        decode_len = (u8_t)(decode_len - 4);
                        next_val_offset = (u16_t)(val_offset + 4);
                        if (next_val_offset < val_offset)
                        {
                            /* overflow */
                            return ERR_BUF;
                        }
                        val_offset = next_val_offset;
                        decode_idx++;
                        goto decode_next;
                    }
                    else if (decode_len == 4)
                    {
                        value = lwip_ntohl(value);
                    }
                    else
                    {
                        LWIP_ERROR("invalid decode_len", decode_len == 1, return ERR_VAL;);
                        value = ((u8_t*)&value)[0];
                    }
                    dhcp_got_option(dhcp, decode_idx);
                    dhcp_set_option_value(dhcp, decode_idx, value);
                }
            }
        }
        if (offset >= q->len)
        {
            offset = (u16_t)(offset - q->len);
            offset_max = (u16_t)(offset_max - q->len);
            if (offset < offset_max)
            {
                q = q->next;
                LWIP_ERROR("next pbuf was null", q != NULL, return ERR_VAL;);
                options = (u8_t*)q->payload;
            }
            else
            {
                /* We've run out of bytes, probably no end marker. Don't proceed. */
                return ERR_BUF;
            }
        }
    }
    /* is this an overloaded message? */
    if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_OVERLOAD))
    {
        u32_t overload = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_OVERLOAD);
        dhcp_clear_option(dhcp, DHCP_OPTION_IDX_OVERLOAD);
        if (overload == DHCP_OVERLOAD_FILE)
        {
            parse_file_as_options = 1;
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded file field\n"));
        }
        else if (overload == DHCP_OVERLOAD_SNAME)
        {
            parse_sname_as_options = 1;
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded sname field\n"));
        }
        else if (overload == DHCP_OVERLOAD_SNAME_FILE)
        {
            parse_sname_as_options = 1;
            parse_file_as_options = 1;
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded sname and file field\n"));
        }
        else
        {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("invalid overload option: %d\n", (int)overload));
        }
    }
    if (parse_file_as_options)
    {
        /* if both are overloaded, parse file first and then sname (RFC 2131 ch. 4.1) */
        parse_file_as_options = 0;
        options_idx = DHCP_FILE_OFS;
        options_idx_max = DHCP_FILE_OFS + DHCP_FILE_LEN;
#if LWIP_DHCP_BOOTP_FILE
        file_overloaded = 1;
#endif
        goto again;
    }
    else if (parse_sname_as_options)
    {
        parse_sname_as_options = 0;
        options_idx = DHCP_SNAME_OFS;
        options_idx_max = DHCP_SNAME_OFS + DHCP_SNAME_LEN;
        goto again;
    }
#if LWIP_DHCP_BOOTP_FILE
    if (!file_overloaded)
    {
        /* only do this for ACK messages */
        if (dhcp_option_given(dhcp, DHCP_OPTION_IDX_MSG_TYPE)
            && (dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_MSG_TYPE) == DHCP_ACK))
            /* copy bootp file name, don't care for sname (server hostname) */
            if (pbuf_copy_partial(p, dhcp->boot_file_name, DHCP_FILE_LEN - 1, DHCP_FILE_OFS) != (DHCP_FILE_LEN - 1))
            {
                return ERR_BUF;
            }
        /* make sure the string is really NULL-terminated */
        dhcp->boot_file_name[DHCP_FILE_LEN - 1] = 0;
    }
#endif /* LWIP_DHCP_BOOTP_FILE */
    return ERR_OK;
}

/**
 * If an incoming DHCP message is in response to us, then trigger the state machine
 */
static void dhcp_recv(void* arg, struct udp_pcb* pcb, struct pbuf* p, const ip_addr_t* addr, u16_t port)
{
    struct netif* netif = ip_current_input_netif();
    struct dhcp* dhcp = netif_dhcp_data(netif);
    struct dhcp_msg* reply_msg = (struct dhcp_msg*)p->payload;
    u8_t msg_type;
    u8_t i;
    struct dhcp_msg* msg_in;

    LWIP_UNUSED_ARG(arg);

    /* Caught DHCP message from netif that does not have DHCP enabled? -> not interested */
    if ((dhcp == NULL) || (dhcp->pcb_allocated == 0))
    {
        goto free_pbuf_and_return;
    }

    LWIP_ASSERT("invalid server address type", IP_IS_V4(addr));

    LWIP_DEBUGF(
        DHCP_DEBUG | LWIP_DBG_TRACE,
        ("dhcp_recv(pbuf = %p) from DHCP server %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F " port %" U16_F "\n",
         (void*)p,
         ip4_addr1_16(ip_2_ip4(addr)),
         ip4_addr2_16(ip_2_ip4(addr)),
         ip4_addr3_16(ip_2_ip4(addr)),
         ip4_addr4_16(ip_2_ip4(addr)),
         port));
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("pbuf->len = %" U16_F "\n", p->len));
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("pbuf->tot_len = %" U16_F "\n", p->tot_len));
    /* prevent warnings about unused arguments */
    LWIP_UNUSED_ARG(pcb);
    LWIP_UNUSED_ARG(addr);
    LWIP_UNUSED_ARG(port);

    if (p->len < DHCP_MIN_REPLY_LEN)
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("DHCP reply message or pbuf too short\n"));
        goto free_pbuf_and_return;
    }

    if (reply_msg->op != DHCP_BOOTREPLY)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
            ("not a DHCP reply message, but type %" U16_F "\n", (u16_t)reply_msg->op));
        goto free_pbuf_and_return;
    }
    /* iterate through hardware address and match against DHCP message */
    for (i = 0; i < netif->hwaddr_len && i < LWIP_MIN(DHCP_CHADDR_LEN, NETIF_MAX_HWADDR_LEN); i++)
    {
        if (netif->hwaddr[i] != reply_msg->chaddr[i])
        {
            LWIP_DEBUGF(
                DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                ("netif->hwaddr[%" U16_F "]==%02" X16_F " != reply_msg->chaddr[%" U16_F "]==%02" X16_F "\n",
                 (u16_t)i,
                 (u16_t)netif->hwaddr[i],
                 (u16_t)i,
                 (u16_t)reply_msg->chaddr[i]));
            goto free_pbuf_and_return;
        }
    }
    /* match transaction ID against what we expected */
    if (lwip_ntohl(reply_msg->xid) != dhcp->xid)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
            ("transaction id mismatch reply_msg->xid(%" X32_F ")!=dhcp->xid(%" X32_F ")\n",
             lwip_ntohl(reply_msg->xid),
             dhcp->xid));
        goto free_pbuf_and_return;
    }
    /* option fields could be unfold? */
    if (dhcp_parse_reply(p, dhcp) != ERR_OK)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("problem unfolding DHCP message - too short on memory?\n"));
        goto free_pbuf_and_return;
    }

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("searching DHCP_OPTION_MESSAGE_TYPE\n"));
    /* obtain pointer to DHCP message type */
    if (!dhcp_option_given(dhcp, DHCP_OPTION_IDX_MSG_TYPE))
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
            ("DHCP_OPTION_MESSAGE_TYPE option not found\n"));
        goto free_pbuf_and_return;
    }

    msg_in = (struct dhcp_msg*)p->payload;
    /* read DHCP message type */
    msg_type = (u8_t)dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_MSG_TYPE);
    /* message type is DHCP ACK? */
    if (msg_type == DHCP_ACK)
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_ACK received\n"));
        /* in requesting state? */
        if (dhcp->state == DHCP_STATE_REQUESTING)
        {
            dhcp_handle_ack(netif, msg_in);
#if DHCP_DOES_ARP_CHECK
            if ((netif->flags & NETIF_FLAG_ETHARP) != 0)
            {
                /* check if the acknowledged lease address is already in use */
                dhcp_check(netif);
            }
            else
            {
                /* bind interface to the acknowledged lease address */
                dhcp_bind(netif);
            }
#else
            /* bind interface to the acknowledged lease address */
            dhcp_bind(netif);
#endif
        }
        /* already bound to the given lease address? */
        else if (
            (dhcp->state == DHCP_STATE_REBOOTING) || (dhcp->state == DHCP_STATE_REBINDING)
            || (dhcp->state == DHCP_STATE_RENEWING))
        {
            dhcp_handle_ack(netif, msg_in);
            dhcp_bind(netif);
        }
    }
    /* received a DHCP_NAK in appropriate state? */
    else if (
        (msg_type == DHCP_NAK)
        && ((dhcp->state == DHCP_STATE_REBOOTING) || (dhcp->state == DHCP_STATE_REQUESTING)
            || (dhcp->state == DHCP_STATE_REBINDING) || (dhcp->state == DHCP_STATE_RENEWING)))
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_NAK received\n"));
        dhcp_handle_nak(netif);
    }
    /* received a DHCP_OFFER in DHCP_STATE_SELECTING state? */
    else if ((msg_type == DHCP_OFFER) && (dhcp->state == DHCP_STATE_SELECTING))
    {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_OFFER received in DHCP_STATE_SELECTING state\n"));
        /* remember offered lease */
        dhcp_handle_offer(netif, msg_in);
    }

free_pbuf_and_return:
    pbuf_free(p);
}

/**
 * Create a DHCP request, fill in common headers
 *
 * @param netif the netif under DHCP control
 * @param dhcp dhcp control struct
 * @param message_type message type of the request
 */
static struct pbuf* dhcp_create_msg(struct netif* netif, struct dhcp* dhcp, u8_t message_type, u16_t* options_out_len)
{
    u16_t i;
    struct pbuf* p_out;
    struct dhcp_msg* msg_out;
    u16_t options_out_len_loc;

#ifndef DHCP_GLOBAL_XID
    /** default global transaction identifier starting value (easy to match
     *  with a packet analyser). We simply increment for each new request.
     *  Predefine DHCP_GLOBAL_XID to a better value or a function call to generate one
     *  at runtime, any supporting function prototypes can be defined in DHCP_GLOBAL_XID_HEADER */
#if DHCP_CREATE_RAND_XID && defined(LWIP_RAND)
    static u32_t xid;
#else  /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
    static u32_t xid = 0xABCD0000;
#endif /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
#else
    if (!xid_initialised)
    {
        xid = DHCP_GLOBAL_XID;
        xid_initialised = !xid_initialised;
    }
#endif
    LWIP_ERROR("dhcp_create_msg: netif != NULL", (netif != NULL), return NULL;);
    LWIP_ERROR("dhcp_create_msg: dhcp != NULL", (dhcp != NULL), return NULL;);
    p_out = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dhcp_msg), PBUF_RAM);
    if (p_out == NULL)
    {
        LWIP_DEBUGF(
            DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
            ("dhcp_create_msg(): could not allocate pbuf\n"));
        return NULL;
    }
    LWIP_ASSERT(
        "dhcp_create_msg: check that first pbuf can hold struct dhcp_msg",
        (p_out->len >= sizeof(struct dhcp_msg)));

    /* DHCP_REQUEST should reuse 'xid' from DHCPOFFER */
    if ((message_type != DHCP_REQUEST) || (dhcp->state == DHCP_STATE_REBOOTING))
    {
        /* reuse transaction identifier in retransmissions */
        if (dhcp->tries == 0)
        {
#if DHCP_CREATE_RAND_XID && defined(LWIP_RAND)
            xid = LWIP_RAND();
#else  /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
            xid++;
#endif /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
        }
        dhcp->xid = xid;
    }
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("transaction id xid(%" X32_F ")\n", xid));

    msg_out = (struct dhcp_msg*)p_out->payload;
    memset(msg_out, 0, sizeof(struct dhcp_msg));

    msg_out->op = DHCP_BOOTREQUEST;
    /* @todo: make link layer independent */
    msg_out->htype = LWIP_IANA_HWTYPE_ETHERNET;
    msg_out->hlen = netif->hwaddr_len;
    msg_out->xid = lwip_htonl(dhcp->xid);
    /* we don't need the broadcast flag since we can receive unicast traffic
       before being fully configured! */
    /* set ciaddr to netif->ip_addr based on message_type and state */
    if ((message_type == DHCP_INFORM) || (message_type == DHCP_DECLINE) || (message_type == DHCP_RELEASE)
        || ((message_type == DHCP_REQUEST) && /* DHCP_STATE_BOUND not used for sending! */
            ((dhcp->state == DHCP_STATE_RENEWING) || dhcp->state == DHCP_STATE_REBINDING)))
    {
        ip4_addr_copy(msg_out->ciaddr, *netif_ip4_addr(netif));
    }
    for (i = 0; i < LWIP_MIN(DHCP_CHADDR_LEN, NETIF_MAX_HWADDR_LEN); i++)
    {
        /* copy netif hardware address (padded with zeroes through memset already) */
        msg_out->chaddr[i] = netif->hwaddr[i];
    }
    msg_out->cookie = PP_HTONL(DHCP_MAGIC_COOKIE);
    /* Add option MESSAGE_TYPE */
    options_out_len_loc = dhcp_option(0, msg_out->options, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
    options_out_len_loc = dhcp_option_byte(options_out_len_loc, msg_out->options, message_type);
    if (options_out_len)
    {
        *options_out_len = options_out_len_loc;
    }
    return p_out;
}

/**
 * Add a DHCP message trailer
 *
 * Adds the END option to the DHCP message, and if
 * necessary, up to three padding bytes.
 */
static void dhcp_option_trailer(u16_t options_out_len, u8_t* options, struct pbuf* p_out)
{
    options[options_out_len++] = DHCP_OPTION_END;
    /* packet is too small, or not 4 byte aligned? */
    while (((options_out_len < DHCP_MIN_OPTIONS_LEN) || (options_out_len & 3)) && (options_out_len < DHCP_OPTIONS_LEN))
    {
        /* add a fill/padding byte */
        options[options_out_len++] = 0;
    }
    /* shrink the pbuf to the actual content length */
    pbuf_realloc(p_out, (u16_t)(sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + options_out_len));
}

/** check if DHCP supplied netif->ip_addr
 *
 * @param netif the netif to check
 * @return 1 if DHCP supplied netif->ip_addr (states BOUND or RENEWING),
 *         0 otherwise
 */
u8_t dhcp_supplied_address(const struct netif* netif)
{
    if ((netif != NULL) && (netif_dhcp_data(netif) != NULL))
    {
        struct dhcp* dhcp = netif_dhcp_data(netif);
        return (dhcp->state == DHCP_STATE_BOUND) || (dhcp->state == DHCP_STATE_RENEWING)
               || (dhcp->state == DHCP_STATE_REBINDING);
    }
    return 0;
}

#endif /* LWIP_IPV4 && LWIP_DHCP */
